Activated vitamin D3 derivatives regulate bone remodeling, consisting of bone formation and bone resorption, and show bone a density-increasing effect. Thus, they are being used as a valuable therapeutic agent for osteoporosis. However, these active vitamin D3 derivatives, 1α,25-dihydroxyvitamin D3 for example, do not necessarily show a satisfactory amount of increase in the bone mineral density. When the dose is increased in order to increase the bone mineral density, there occurs an increase in a serum calcium value rather than further increase in the bone mineral density, causing elevation of the serum calcium value by 1 mg/dL or more, a value considered as one of the criteria for clinical undesirability. Thus, there are occasional cases where a sufficient bone mineral density-increasing effect is not obtained (International Publication No. WO 01/62723). Therefore, there is an earnest desire for an activated vitamin D3 derivative which exhibits a strong bone mineral density-increasing effect without increasing the serum calcium value. Heretofore, there have been synthesized a multitude of vitamin D3 derivatives in an effort to obtain such a derivative, but there has not yet been found any derivative which has a satisfactory profile.